A two-stage heating geothermal energy system using geothermal energy refers to a system able to provide cooling and heating as well as hot water to users using heat obtained by heat exchange conducted underground. Disclosed as examples of the two-stage heating geothermal energy system are Korean Patent No. 10-0998483 (titled: “MULTI-MODULE COOLING AND HEATING SYSTEM USING GEOTHERMAL HEAT EXCHANGE PUMP”), Korean Patent No. 10-1052465 (titled: “DUAL-TYPE HEAT PUMP SYSTEM USING HEAT TRANSFER MEDIUM AND REFRIGERANT”), Korean Patent No. 10-0900441 (titled: “HEAT PUMP COOLING AND HEATING SYSTEM USING GEOTHERM”), and the like.
Condensation heat created while a geothermal heat pump is providing cooling to a user side has been directed to the underground to be discarded. In such conventional two-stage heating geothermal energy systems using geothermal energy, such condensation heat is used as a heat source of a hot water tank through a separate bypass pipe or is used for auxiliary heating through a floor heating coil. However, the use of condensation heat as above has the following problems.
First, the temperature of heat discarded from the geothermal heat pump to the underground is about 25° C. to about 30° C., which has a significant difference from the temperature of hot water necessary for hot water supply or auxiliary heating, which is about 40° C. to about 50° C. Since repetitive heating is necessary to raise the temperature to a desirable temperature, a large amount of energy is spent in heating.
Second, since the temperature of hot water necessary for hot water supply or auxiliary heating is about 40° C. to about 50° C., a condensation temperature necessary for the geothermal heat pump must be significantly raised to a level of about 35° C. to about 50° C., which is the temperature of a typical operation. This causes an increase in the condensation temperature of Freon, thereby leading to an insignificant increase in the compression ratio of a compressor and an insignificant decrease in the efficiency (COP) of the geothermal heat pump. Accordingly, the amount of power consumed for the cooling operation of the geothermal heat pump is significantly increased.
Furthermore, a separate heat pump for hot water supply is not provided. In a heating mode in the winter, hot water produced for heating by the geothermal heat pump must be divided for heating and hot water supply, thereby reducing the usability of a geothermal heat source. In addition, when the temperature of water for heating is different from the temperature of water for hot water supply, it may be difficult to perform independent temperature control.